Effect of pre-treatment of synergists on the toxicity of insecticides to Spodoptera uitura (Fabricius).

The pre treutment of different synergists before the application of insecticide proved synergistic over the period of time (up to 24hr). The toxicity of cypermethrin,when pre- treated with different synergist showed wide variation in mortality of Spodoptera litura larvae. The highest mortality of 83.33% was observed/i when pipronyl butoxide (PBO) was applied 8hr before the application of cypermethrin. PBO, dillapiole and dihydrodillapiole increased more than 50% fenvalerate induced mortality from 2–14, 6–14 and 4–8 hr, respectively at post-treatment. The highest mortality of 80% by lambda cyhalothrin was observed at 6 and 8 hr post-treatment of PBO and dihydrodillapiole. The toxicity of profenophos increased with pre-treatment of each of the synergists. The highest mortality of 70% and 76.67% was observed at 8 and 10 hr post-treatment of dillapiole and PBO respectively. The mortality obtained between 6 to 12 hr pretreatment of I'BO, and dillapiole varied from 53.33 to 70% and 63.33 to 46.67%. There was a highly significant increase in the mortality due to cypermethrin, fenvaleratc, lambda-cyhalothrin and profenophos when pre-treatment at 6 to 10 hrs with PBO was done. A delay of 8–10 hr prior to insecticide application was beneficial in case of dihydrodillapiole whereas a delay of 6–14 hr following pre-treatment of dillapiole increased the synergistic effects with various insecticides.